#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=2e5+100;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL fa[maxn];
LL find(LL x){
    if(fa[x]!=x) return fa[x]=find(fa[x]);
    else return fa[x];
}
int main(void)
{
  cin.tie(0);std::ios::sync_with_stdio(false);
  LL n,m;cin>>n>>m;
  for(LL i=1;i<=n;i++) fa[i]=i;
  for(LL i=1;i<=m;i++){
    LL u,v;cin>>u>>v;
    LL a=find(u);LL b=find(v);
    if(a<b) fa[a]=b;
    else fa[b]=a;
  }
  LL maxv=find((LL)1);
  LL ans=0;
  for(LL i=1;i<=n;i++){
    if(i<=maxv){
        LL tmp=find(i);
       /// cout<<"i="<<i<<" "<<"tmp="<<tmp<<" "<<"maxv="<<maxv<<"\n";
        if(tmp!=maxv){
            ans++;
            if(tmp>maxv){
                fa[maxv]=tmp;
                maxv=tmp;
            }
            else fa[tmp]=maxv;
        }
    }
    else maxv=find(i);
  }
  cout<<ans<<"\n";
return 0;
}
